Acoustical Physics最新文献

Under laboratory conditions, experimental verification of the developed algorithms for reconstructing low-contrast bottom layers during their coherent sensing was carried out. The algorithms use parametric models for generating signals reflected from a layered half-space in the form of a set of elastic layers. To solve the problem at the Department of Acoustics of Nizhny Novgorod State University, an experimental setup was created for the formation, emission, and reception of high-resolution sound pulses reflected from a set of elastic layers placed in a tank of water. The experimental study showed the possibility of using the coherent sensing method for layered media with relatively similar acoustic parameters. Processing of the data obtained resulted in good agreement between the developed computational model of probing acoustic pulse signals reflected from a layered bottom and the physical modeling data. It is shown that analysis of the plane of the geoacoustic parameters of a specific problem using the developed numerical model makes it possible to assess the capabilities of a promising method for coherent diagnostics of low-contrast bottom layers.

An elastic medium with inclusions that are small compared to the sound wavelength and differ in density is considered. If the inclusions are resonators that respond equally to the influence of waves coming from different directions, then the effective density of the medium in a certain frequency band becomes negative. If the direction of the dipole moment of the resonators is fixed, then the medium with inclusions has an anisotropic effective density. The Helmholtz equation for such a medium was obtained, and the field of a point source was studied.

We consider the problem of estimating the position of a local inhomogeneity on a stationary acoustic path between a single sound source and vertical receiving array in a shallow water waveguide in the presence of background disturbances. A local bottom rise and a soliton-like internal wave are chosen as model inhomogeneities. It is proposed to determine the distance from the source to the inhomogeneity by cepstral analysis of the amplitude of the first waveguide mode isolated on the array, with preliminary deformation of the frequency axis. Numerical modeling is used to study the stability of this approach in the presence of several local inhomogeneities or additional disturbances: bottom slope, background internal waves, wind waves, and bottom irregularities. Estimates of the signal-to-noise ratio required to implement the approach are pro-vided.

The results of measuring cavitation thresholds and some hydrological and hydrochemical parameters of seawater in various areas of the World Ocean are presented and discussed. The stable temporal variability of the cavitation thresholds on time scales of several days is shown. The daily, semidaily, and other periodicities of changes in magnitude of cavitation thresholds are revealed.

The combined influence of random internal waves and developed wind waves on the coherence and efficiency of spatial processing of narrowband acoustic signals in shallow water is studied analytically and numerically. A theoretical model is proposed for the correlation matrix of a multimode signal at the aperture of a horizontal array, using the difference in the spatiotemporal scales of acoustic field fluctuations caused by wind waves and internal waves. The results of numerical modeling for hydrological conditions in summer are presented. The array gain is analyzed for three spatial processing methods: phased array, optimal linear processing, and optimal quadratic processing. The main focus is on the dependence of the array gain on the intensity of wind waves and distance R between the source and the array. It is shown that, despite summer hydrology, wind waves can have a significant impact on the gain of a horizontal array over a wide range of distances R ~ 10–100 km.

A method is proposed for quickly estimating the sonic boom characteristics from supersonic passenger aircraft under standard atmospheric conditions. The piecewise linear temperature profile and absence of atmospheric wind make it possible to completely reduce the problem of the geometry of sonic boom wave propagation to an algebraic form. For acoustic pressure, an analytical solution is formulated using the nonlinear geometrical acoustics approach. The dependence of the geometry of sonic boom wave propagation on the cruising flight parameters of a supersonic passenger aircraft is analyzed. Under the conditions of SBPW (Sonic Boom Prediction Workshop) 2020, the overpressure signatures on the ground from the X-59 demonstrator were calculated.